Correlation of current-voltage characteristics of step-edge YBa2Cu3O7 Josephson junctions with the step angle

摘要

Abstract: We report on a systematic study of the transport characteristics of YBa$-2$/Cu$-3$/O$-7$/ (YBCO) step-edge Josephson junctions as a function of the step angle. The microstructure of a YBCO film depends very critically on the step angle $alpha in a SrTiO$-3$/ or LaAlO$-3$/ substrate. Briefly, on shallow steps (0 $LS $alpha $LS 44$DGR) the film grows epitaxially across the step. On steep steps (46$DGR $LS $alpha $LS 85$DGR) two grain boundaries occur on the step. In this paper it is shown that the I-V curves of the step-edge junction reflect the microstructure of the YBCO film on the step. The I-V curves on shallow steps are of flux-flow type. On 45$DGR steps there are several Josephson junctions with different critical currents, while on steep steps two critical currents are found in the I-V curve. Summarizing all data, we conclude that the grain boundaries formed on steep steps are responsible for the Josephson behaviour of the junctions. !8